1. Field of the Invention
This invention relates generally to compatibilizing two incompatible polymer systems, namely: polyolefins and styrene copolymers and polymer blends. The invention also relates to compounded, compatiblized polyolefin-styrene copolymer or polymeric blend compositions and specific articles of manufacture produced therefrom.
2. State of the Art
Polymeric blends have been known for years. Typically, blends of polymers result in a material which combines the poorest properties of the constituents. This is a result of the incompatibility of the constituent polymers resulting in little, if any, adhesion at the interface between the different constituent polymers. Furthermore, this incompatibility stems in part from the structure of the individual polymers. Thermodynamically, one polymeric phase has more of an affinity for itself than for the other polymeric phase so that intermolecular forces between the two polymers is weak. For example, a blend of a polar polymer and a non-polar polymer would result in an incompatible system demonstrating poor physical properties for lack of wetting and adhesion at the interface. Even in cases when the polarity of the polymers in a blend are similar, compatibility is generally not achieved because the entropy change upon mixing of high polymers is not favorable.
Such incompatibility problems may be overcome through the use of a compatibilizing agent. A compatibilizing agent is a material which, on a molecular scale, has particular regions which are compatible with each of the incompatible constituent polymers. Such compatibilizing agents typically surround one polymeric phase providing a chemical or physical bridge to the other polymeric phase. Insomuch as portions of the compatibilizing agent are compatible with each of the constituent polymers, the bonding between the two incompatible polymeric phases is effectively enhanced through this intermediate compatibilizing phase. Such a system of incompatible polymers coupled by a compatibilizing agent results in a material which advantageously combines the more desirable properties of the constituent polymers. Lindsey et al., J. Appl. Polymer Sci., Vol. 26, 1-8 (1981) describes a method of reclaiming mixed immiscible polymers by employing a compatibilizing agent. The system studied was a high density polyethylene (HDPE) and polystyrene (PS) and styrene-ethylene-butene-1-styrene (SEBS) copolymer as the compatibilizing agent. These ternary blends were found to possess a considerable improvement in the balance of mechanical properties over a binary blend of high density polyethylene and polystyrene.
Bartlett et al., Modern Plastics, Dec. 1981, 60-62 describes a system comprising polypropylene, polystyrene and styrene-ethylene-butene-1-styrene as a compatibilizer. This work focused on those parameters that affected the extent of the polypropylene crystallinity.
Polystyrene homopolymers and copolymers compatibilized with polyolefins have been available for several years. Furthermore, molded articles have been produced from such compatibilized polymer compositions. For example, U.S. Pat. No. 4,386,187 discloses a thermoformable polymer blend of a polyolefin, a styrene polymer and a styrenic block copolymer rubber. While a number of styrene polymers and copolymers are disclosed, a copolymer of styrene and maleic anhydride is not.
U.S. Pat. No. 4,647,509 discloses a multilayer thermoformable packaging material comprising a first layer of a) a vinylidene chloride polymer, b) an incompatible polymer, e.g., polyesters and nylons, and c) a compatibilizing agent and a second layer of a) a blend of an olefin polymer, a styrenic polymer, and a compatibilizing polymer, and b) scrap material produced from the first and second layers.
U.S. Pat. No. 4,107,130 discloses a multicomponent polymer blend comprised of a polyolefin, a selectively hydrogenated monoalkenyl arenediene block copolymer, and at least one dissimilar engineering thermoplastic resin.
None of the foregoing disclosures, teach, for example, a polyolefin compatiblized with a copolymer of styrene and maleic anhydride, nor mixtures of styrene polymers and copolymers such as a polystyrene, polyphenylene oxide, elastomer blend, such as General Electric's NORYL.RTM.. These particular polystyrene systems are unique in their chemistry as well as their physical properties.